ABSTRACT: Dolomitization of the Devonian Dunedin, Keg River and Slave Point Formations of Northeast British Columbia

NADJIWON, LISA M., University of Waterloo, Waterloo, ON, Canada; MORROW, DAVID W., Geological Survey of Canada, Calgary, AB, Canada; and CONIGLIO, MARIO, University of Waterloo, Waterloo, ON, Canada

The Keg River and Slave Point formations represent an extensive barrier reef complex along the northwest edge of the Elk Point Basin. Important hydrocarbon reservoirs, such as the Clarke Lake and Yoyo fields, were created in these rocks through hydrothermal dolomitization. Peritidal and subtidal platform carbonates of the correlative Dunedin Formation were deposited to the west of the barrier complex on the MacDonald Shelf. These strata are well exposed in the Rocky Mountains, whereas the Keg River and Slave Point formations lie in the subsurface to the east. The edge of the barrier is also exposed in places along the outcrop belt.

Both formations exhibit similar diagenetic facies, in which the original limestone was altered to coarsely crystalline replacive dolostone and white sparry dolomite cement. Late stage precipitates occurring in some large remaining open pore spaces include coarsely crystalline calcite and prismatic quartz crystals. This diagenetic assemblage is concentrated within facies of originally characterized by high primary porosity, and typically containing abundant reef-forming organisms. Preliminary fluid inclusion data indicate that dolomitization occurred through circulation of hot fluids, later followed by a cooler and less saline fluid precipitating calcite and quartz. Additional work will concentrate on transmitted light and cathodoluminescence petrography and stable carbon and oxygen isotope geochemistry of rocks from outcrops and the subsurface. Combined with results from earlier subsurface investigations, this project will provide new insights into the controls on hydrothermal dolomite reservoirs, and may help refine strategies for hydrocarbon exploration in the Devonian of northeast British Columbia.

Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada